Japan’s Hayabusa 2 probe to fire pellet at asteroid to obtain samples

The surface of Ryugu. Hayabusa 2 caught up with the asteroid after a three-and-a-half year journey in June last year.
Photograph: Jaxa Handout/EPA

A Japanese spacecraft is to attempt an audacious smash-and-grab manoeuvre on a speeding asteroid in an attempt to collect samples and return them to Earth.

The Hayabusa 2 probe is due to touch down on the asteroid Ryugu at 11pm GMT on Thursday. It will then fire a tantalum pellet into the surface to kick up dust and grains that it will try to capture.

The operation will be more of a delicate kiss than a hard touchdown. The spacecraft will barely touch the asteroid as it seeks to gather the dislodged debris with an instrument named the Sampler Horn that hangs from its underbelly.

“It’s very challenging because it all has to be done autonomously,” said Ian Franchi, an astronomer at the Open University in Milton Keynes. “There is so little gravity, and there are so many boulders on the surface.”

Ryugu is less than a kilometre across and its density is such that its gravitational pull is one sixty-thousandth that on Earth. In such meagre gravity, material dislodged by Hayabusa’s bullet should bounce up the 1.5-metre Sampler Horn into a chamber inside the probe.

Hayabusa 2 caught up with Ryugu in June last year after a three-and-a-half-year journey to intercept it. Mission controllers at the Japanese space agency had planned to touch down in October, but delayed the attempt after cameras revealed the surface to be far rockier than expected.

Scientists on the mission have spent the past few months performing lab tests with replica equipment to ensure the spacecraft still has a chance of collecting some of the asteroid.

Hayabusa 2 will fire a 5g pellet at more than 650mph into the asteroid’s surface. If all goes to plan, the probe will collect up to 10g of grains thrown up by the impact, before retreating to a safe distance. The material will then be stored onboard until the spacecraft returns to its landing site in Woomera, South Australia, in 2020 after a journey of more than 3bn miles.

The asteroid belongs to a family of space rocks that are the most primitive building blocks of the solar system. “This is the material that didn’t get swept up into planets, it got left behind,” said John Bridges, a professor of planetary science at the University of Leicester. “The reason we want to study it is that this is what material was like at year zero.”

Similar material falls to Earth as meteorites, but it is battered and burned as it tears through the atmosphere and quickly becomes contaminated when it thumps into the ground. The asteroid material from Hayabusa 2 will show scientists what meteorite material is like before it plunges to Earth.

Analysis of the asteroid grains may shed light on where Earth got its water. Many scientists once thought that comets brought water to Earth, but studies have shown that comet water has a different chemical signature to that found on Earth. “This is all about understanding where water existed in [the] solar system, what the signature of that water was, and can we say better where Earth’s water came from,” said Franchi.

Asteroids also carry organic material that may be important for the emergence of life. The advantage of having pristine grains to study is that, unlike fragments of meteorites, they will not be contaminated with organic material from Earth.

The Japanese space agency is saving its most dramatic act for the spring. As early as March, Hayabusa 2 will detonate an explosive that rips a new crater in Ryugu. The spacecraft will then descend once more to collect fresh material from a crater basin that has not been battered by billions of years in space.

“It all looks very promising for the mission,” said Bridges, who will be one of the scientists in line to study any material Hayabusa 2 brings home. “It’s a remarkable achievement.”